Digital Dash MPG Accuracy
Digital Dash MPG Accuracy
Okay, so this is a question for the digital dash Beretta owners:
How accurate have you found the MPG display on your digital display to be?
I currently have three Berettas with the digital dash, but one car isn't running right now (the V-8 Indy), and one doesn't have the ECM controlling the engine (the '89 3800 SC GTU) and therefore doesn't have MPG data to display, so only the Yellow Indy (stock 3.1 MPFI, auto trans) that I have is displaying the MPG. I have thusfar only filled the tank on the car once since I bought it, and with swapping-out the instrument cluster (I temporarily installed the spare cluster that came with the car after modifying the backlighting to yellow instead of orange, but finally modified the original cluster and reinstalled that one) I haven't really had a chance to get a solid feel for the accuracy of the display. With the two of my '85 Nissan 300ZX's (one is now gone
), both had the digital gauge package, and the MPG displays were 'dead-on balls accurate (it's an industry term 
)'.
The previous owner of my Yellow Indy said he was getting better than 30 MPG with the car, and so far, that is what my "Average MPG" has been saying, with both clusters. I first saw ~33 average with a mix of back-roads country-side and a little bit of in-town driving, and more recently (after swapping the original cluster back in) I have an average 30.5 MPG, with pretty much the same type of driving with the addition of some, we'll say 'spirited,' driving along twisty, hilly roads for several miles that yielded some MPG on the very low 20s that the more gentle driving has had to compensate for to achieve the 30.5 MPG over the last 100 miles or so.
So a second question could be (and yes, it has been asked before, but it is okay I think to keep asking it as times change) what kinds of MPG are people getting these days?
-My Indy has 150k miles, with a newer engine allegedly installed ~50k miles ago. I'll take a guess and say ~31 MPG with this one.
-My '89 3800 SC 5-speed GTU gets about 22 MPG, probably better if I could keep my foot out of it.
-And my '95 Z-26 (3100 auto with a 3400 top-end) got about the same as the GTU, maybe a little less with severe mountain-driving.
-The '90 'T-Type' turbo 5-speed 'Retta saw about 30 MPG highway and 25-27 MPG city before I put the 3.4 semi-built engine back in, I have no idea what she is getting now.
-The V-8 Indy hasn't run for years, and I don't have a clue what her MPG is.
Just for comparison, my '97 Z-24 2.4 Twin Cam turbo five-speed Cavvy gets anywhere from low teens to low thirties, depending on how badly I am beating-up other cars with it, and my old '88 350 Camaro with over 300k miles on the engine saw a very reliable 22.5 city, 26.5 highway (55 or 90, speed didn't matter, so long as it was highway
). The '92 Grand Am with the 2.3 SOHC/auto got just over 30 MPG, even while running on two cylinders (though top speed was also just over 30 
). My '85 turbo 300ZX got 20 city, ~31 highway with the T-tops out, ~29 MPG highway with the tops in and the A/C on 
, and top speed was maybe 130 
. The Toyota in our family with way over 200k miles gets 40+ MPG, and my Kawasaki ZX-11 got better than 50 MPG, even with low warp-speed usage, while my old Kawasaki GP bike only sees a flat 30 MPG city and highway. I could really go on and on, but these are the numbers I am sure of.
How accurate have you found the MPG display on your digital display to be?
I currently have three Berettas with the digital dash, but one car isn't running right now (the V-8 Indy), and one doesn't have the ECM controlling the engine (the '89 3800 SC GTU) and therefore doesn't have MPG data to display, so only the Yellow Indy (stock 3.1 MPFI, auto trans) that I have is displaying the MPG. I have thusfar only filled the tank on the car once since I bought it, and with swapping-out the instrument cluster (I temporarily installed the spare cluster that came with the car after modifying the backlighting to yellow instead of orange, but finally modified the original cluster and reinstalled that one) I haven't really had a chance to get a solid feel for the accuracy of the display. With the two of my '85 Nissan 300ZX's (one is now gone
), both had the digital gauge package, and the MPG displays were 'dead-on balls accurate (it's an industry term )'.The previous owner of my Yellow Indy said he was getting better than 30 MPG with the car, and so far, that is what my "Average MPG" has been saying, with both clusters. I first saw ~33 average with a mix of back-roads country-side and a little bit of in-town driving, and more recently (after swapping the original cluster back in) I have an average 30.5 MPG, with pretty much the same type of driving with the addition of some, we'll say 'spirited,' driving along twisty, hilly roads for several miles that yielded some MPG on the very low 20s that the more gentle driving has had to compensate for to achieve the 30.5 MPG over the last 100 miles or so.
So a second question could be (and yes, it has been asked before, but it is okay I think to keep asking it as times change) what kinds of MPG are people getting these days?
-My Indy has 150k miles, with a newer engine allegedly installed ~50k miles ago. I'll take a guess and say ~31 MPG with this one.
-My '89 3800 SC 5-speed GTU gets about 22 MPG, probably better if I could keep my foot out of it.
-And my '95 Z-26 (3100 auto with a 3400 top-end) got about the same as the GTU, maybe a little less with severe mountain-driving.
-The '90 'T-Type' turbo 5-speed 'Retta saw about 30 MPG highway and 25-27 MPG city before I put the 3.4 semi-built engine back in, I have no idea what she is getting now.
-The V-8 Indy hasn't run for years, and I don't have a clue what her MPG is.
Just for comparison, my '97 Z-24 2.4 Twin Cam turbo five-speed Cavvy gets anywhere from low teens to low thirties, depending on how badly I am beating-up other cars with it, and my old '88 350 Camaro with over 300k miles on the engine saw a very reliable 22.5 city, 26.5 highway (55 or 90, speed didn't matter, so long as it was highway
). The '92 Grand Am with the 2.3 SOHC/auto got just over 30 MPG, even while running on two cylinders (though top speed was also just over 30 ). My '85 turbo 300ZX got 20 city, ~31 highway with the T-tops out, ~29 MPG highway with the tops in and the A/C on , and top speed was maybe 130 . The Toyota in our family with way over 200k miles gets 40+ MPG, and my Kawasaki ZX-11 got better than 50 MPG, even with low warp-speed usage, while my old Kawasaki GP bike only sees a flat 30 MPG city and highway. I could really go on and on, but these are the numbers I am sure of.1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26
Re: Digital Dash MPG Accuracy
The accuracy of these meters, in terms of GM products, is a good rough estimate, but you gotta make sure the sensors are all fully functional and the speedo is correctly calibrated. Mostly the last one is a problem for truck owners, which all of my vehicles have pretty much been. Car owners don't typically change tire sizes very often or at all, unlike truck guys. For instance, I've had 3 different sizes of tire on my 2500HD in the past 2 years, from 31" to 33" in size, which is about the accepted range of a stock height full size 4x4 truck.
Anyway, even my parents 09 GMC Sierra's MPG display is not exactly perfect and I only used the truck with the factory tire package on the truck, so i'm assuming it was as accurate as possible. It wasn't off my much, but it's enough to bother anyone who is measuring MPG down to the last drop.
Anyway, even my parents 09 GMC Sierra's MPG display is not exactly perfect and I only used the truck with the factory tire package on the truck, so i'm assuming it was as accurate as possible. It wasn't off my much, but it's enough to bother anyone who is measuring MPG down to the last drop.
Re: Digital Dash MPG Accuracy
Fuel consumed divided by miles that tank equals a more accurate result. Just saying. LOL
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Re: Digital Dash MPG Accuracy
Not if the ECU is setup properly... The MPG readout is a calculation of what the injector flow rate is, how long the injectors are pulsing and how fast the vehicle is going. With a newer OBDII setup you can actually dial in the MPG readout by tweaking your Injector flow rate numbers to get it spot on... Regarding this setup though, being MPFI there has to be something in there for (MS*Flow)*3 to get a proper number since it's batch fire of three injectors each time, but I don't know that for sure.
All I know is my Legacy gets 22-24mpg average... Boost is addicting...
All I know is my Legacy gets 22-24mpg average... Boost is addicting...
Re: Digital Dash MPG Accuracy
They can be accurate, to a degree, but you are also dealing with a 20+ year old vehicle, with a bunch of old 22 year old electronics n it.
I just know that the modern vehicles, with their many constant calculations and controls, still can't get it right, out of the box. It's a good quick tool for a ballpark figure and the real figure will come out of your fuel usage calculations.
I don't have any experience with the OBD-I setups though, there were some oddball stuff happening in most GM vehicles during that time period (87-91)...like my computer-controlled-carbureter 1988 Caprice Classic with it's rats nest of vacuum hoses and crap.
I just know that the modern vehicles, with their many constant calculations and controls, still can't get it right, out of the box. It's a good quick tool for a ballpark figure and the real figure will come out of your fuel usage calculations.
I don't have any experience with the OBD-I setups though, there were some oddball stuff happening in most GM vehicles during that time period (87-91)...like my computer-controlled-carbureter 1988 Caprice Classic with it's rats nest of vacuum hoses and crap.